1. Field of the Invention
The present invention relates to a video image transfer device for acquiring video signals inputted by a plurality of image pickup devices and making a display device display a video image in accordance with the video signal from each image pickup device and a display system including the video image transfer device.
2. Description of the Related Art
There has been known an image pickup/display system (multiple input system) which makes it possible to simultaneously input video signals from a plurality of image pickup devices (cameras) therein and display a video image in accordance with the video signal from each image pickup device.
In a conventional general multiple input system, such video signals inputted from such plural image pickup devices are displayed on the display section in such a manner that the video signals are switched over by a switching means (for example, a switch) in order to be fed to the display section.
For example, an image pickup apparatus for in-vehicle use, in which a plurality of image signals inputted by a plurality of image pickup devices are switched over to be fed to an output device (Japanese Unexamined Patent Publication, Tokukaihei, No. 7-7653 (published on Jan. 10, 1995), is known.
Except for in-vehicle use, the fields of FA and security have adopted a liquid crystal display device in which video signals from a plurality of image pickup devices (cameras) can be inputted therein and displayed as video images. Each of the video signals is inputted into such a liquid crystal display device at a constant interval (at a constant data transfer speed). Channels for displaying the video images are independently provided.
Unfortunately, the multiple input system of this method cannot display a video image at a refresh rate (frame rate) according to a purpose or a situation because the refresh rate of each video image is fixed. That is, because the conventional multiple input system divides the refresh rate into even portions and assigns each portion to each video image, the refresh rate for each video image is the quotient of the maximum refresh rate of the display device (a total number of the frames which the display device can display in one second) divided by the number of the image pickup devices. For example, a refresh rate for each video image is lowered to 10 frames/sec in the case where the number of image pickup devices is three and the display device can display images at the refresh rate of 30 frames/sec. This can cause in an important video image a dropped frame which is perceptible to a user. Especially for an in-vehicle image pickup/display system, which is used for a driver to check the surroundings of a vehicle, a dropped frame in an important video image is unacceptable in many cases because the dropped frame could lead to a delay in the driver's check of the surroundings of the vehicle. The in-vehicle image pickup/display system for a driver to check the surroundings of a vehicle is required to display an important video image in real time.
In the conventional multiple input system, in addition, the division and assignment of an input bandwidth cannot be performed according to a purpose or a situation to each video signal since the input bandwidth of each video signal for the display device (a data amount per second of each video signal to be inputted into the display device; a bit transfer rate) is fixed. That is, the input bandwidth of each video signal is the quotient of a total input bandwidth of the display device (a total amount of data which can be inputted into the display device in one second) divided by the number of the image pickup devices since the input bandwidth is evenly divided and assigned to each video signal in the conventional multiple input system. Accordingly, the refresh rate and a resolution of each video image are low. Consequently, as described, this could result in a dropped frame, which is perceptible to a user, in an important video image or an insufficient resolution of an important video image.